Generally, when a car door is closed the latch of the door will be engaged with the car body. In order to prevent the door from being opened unintentionally, each car door is installed with a locking device beside the door window. The door can be locked by simply pushing the locking device downwards, this prevents the door from being opened during the time when the car is running, even if the door latch is touched unintentionally. This locking device can insure the driving safety of a car, but its main drawback is that it has to be operated manually (i.e., to push it downwards), thus, it is deemed inconvenient to the driver; especially when the car is running. The car door could be opened and could cause danger to the rider or other cars, if the locking device is not locked properly as a result of negligence. To unlock the locking device, a manual operation is still required to pull up the locking device, and therefore it is deemed inconvenient. Moreover, the locking devices of some cars have to be locked or unlocked with a key, and this is still deemed inconvenient to the user.